1. Field of the Invention
The present invention relates to a terrestrial digital television broadcast signal receiver (hereinafter, abbreviated as TV broadcast signal receiver), and especially relates to a TV broadcast signal receiver which can update an electronic program guide automatically while a user watches no TV program.
2. Description of the Related Art
In a terrestrial digital TV broadcast, information relating to programs such as an electronic program guide (hereinafter, abbreviated as EPG (Electronic Program Guide)) other than picture signal, audio signal, a transmission control signal, and so on is included in the TV broadcast signal transmitted from a TV station of each channel. The EPG includes information relating to a broadcast such as TV programs which are scheduled for transmission in the channel and air time zones or intersections thereof. There is a TV broadcast signal receiver which receives EPG data from the TV broadcast signal transmitted from a TV station of each channel which can be received, to make a synoptic table of the EPGs, and to display the synoptic table on a screen of a display apparatus. A user can easily find and choose a TV program which he/she wants to watch from the synoptic table of the EPGs displayed on the screen of the display apparatus, and can reserve the reception and reproduction or recording of the TV program.
The EPG is included in the TV broadcast signal transmitted from each TV station at a constant time interval. When the user continuously watches a TV program or TV programs of a specific channel, the EPG data of the specific channel is taken into the TV broadcast signal receiver at the constant time interval, so that the EPG data is automatically updated. With respect to the channels that the TV programs thereof are not watched by the user, the EPG data of the channels are not taken and not updated. In the technical standard, the EPG data should include one week of contents. It is usually the case, however, that the EPG data includes contents of about one day or less. Therefore, when the EPG data is not updated, the contents of the EPG are eliminated with passage of time, and finally, all the EPG data may be lost as outdated information. Then, the EPG of the specific channel is not displayed on the screen of the display apparatus.
When the user switches on the TV broadcast signal receiver so as to display the EPG on the screen of the display apparatus after the EPG data of a specific channel or all channels is/are lost, the TV broadcast signal receiver tunes a frequency of a tuner to the channel that has lost its EPG data, and receives the TV broadcast signal of the channel. Then, the EPG data is taken from the received TV broadcast signal, and the EPG of the channel is displayed on the screen of the display apparatus.
By the way, since the EPG data is included in the TV broadcast signal at a constant time interval, a predetermined time is necessary for the EPG data to be received by the TV broadcast signal receiver. Furthermore, when the EPG data of a plurality of channels are lost, it is necessary to take the EPG data about all the channels that have lost their EPG data. Generally, the TV broadcast signal receiver cannot receive TV broadcast signals of a plurality of channels simultaneously, so that a time necessary for taking the EPG data of the channels becomes much longer. Therefore, there is a problem that a constant time lag occurs before the EPG is really displayed on the screen of the display apparatus, after choosing a mode for displaying the EPG on the screen of the display apparatus by operation of the wireless remote controller by the user.
For solving the above-mentioned problem, a conventional TV broadcast signal receiver shown in Japanese Laid-Open Patent Publication No. 2001-136453 automatically sets an update time for taking new EPG data on the basis of information of a delivery plan included in the EPG data previously taken, switches on the electric power when it reaches the update time for taking the EPG data, and switches off the power after setting the next update time. In this conventional TV broadcast signal receiver, the EPG data of a channel to be updated, however, cannot be taken, if the user watches a TV program of a different channel at the update time. Therefore, there is a case that the EPG can not be displayed on a screen of a display apparatus immediately, even when the user tries to display the EPG on the screen of the display apparatus. On the other hand, a time of a TV program which is actually delivered is generally longer than the time interval of the EPG data included in the TV broadcast signal, so most of the contents of the updated EPG data is the same as that of the EPG data previously taken. Therefore, if the EPG data is updated at each time of delivery of the EPG data, electric power used for updating the EPG data is wasted. On the other hand, when menu display is performed to let the user choose either update time among a plurality of update times, not only a display program of the TV broadcast signal receiver becomes complex, but also a setting operation of the update time by the user becomes complex and troublesome.
Another conventional TV broadcast signal receiver shown in Japanese Laid-Open Patent Publication No. 2002-142163 stores EPG data taken in the TV broadcast signal receiver in a nonvolatile memory when an electric power is switched off, and reads out the EPG data stored in the nonvolatile memory so as to display the EPG on a screen of a display apparatus when the electric power is switched on next. The EPG data, however, are eliminated with passage of time as mentioned above. Thus, the EPG cannot be displayed because all of the EPG data may be lost when the electric power has not been switched on during a predetermined period of time.
Still another conventional TV broadcast signal receiver shown in Japanese Laid-Open Patent Publication No. 2004-228992 has two tuners, one is used for receiving a TV broadcast signal of a specific channel which is watched by a user and the other is used for receiving a TV broadcast signal of a channel which is not watched by the user so as to take the EPG data therefrom. The TV broadcast signal receiver having two tuners, however, is expensive, and is wasteful because one of the tuners is used for receiving only the EPG data.